US App. Pub. 2011/0087444 to Volker (hereinafter the '444 publication) is directed to a “pig” for crawling through the bore of a pipe and performing ultrasound inspection of the inner pipe surface. The reference discloses an algorithm for imaging the pipe surface based on backscatter signals. The '444 publication involves Fermat's principle to determine sound paths with the shortest travel time. The modeling involves first building a grid and determining travel time for each point in the grid. The '444 reference requires scanning a pipe from the inside, where the primary information to be ascertained is 3D information about the inner surface of the pipe. This does not solve than the problem of accurately modeling the inner surface of a pipe using a scanning apparatus positioned on the outer surface.
U.S. Pat. No. 7,685,878 to Brandstrom (hereinafter the '878 patent) relates to a device for rotating a pair of ultrasound transducers around a pipe circumference for pipe weld inspection. It allows the cables and other apparatus extending away from the transducers to remain stationary, extending away in only a single direction. '878 teaches an apparatus which can be mounted on the pipe at the position adjacent the weld and which carries the transducers and rotates those transducers around the pipe, bearing in mind that effective access to the pipe is generally only available from one side of the pipe.
Two transducers are rotated around a circumferential location on a cylindrical body for structural testing of the body, carried on a mounting and drive apparatus including a magnetic attachment which can be manually brought up to a pipe from one side only for fixed connection to the pipe on that side at a position axially spaced from a weld. A collar shaped support for the pair of transducers is formed of a row of separate segments which wrap around the pipe from the one side and is rotated around the axis of the pipe to carry the transducer around the circumferential weld. The segments carry rollers to roll on the surface and are held against the pipe by magnets. The transducers are carried on the support in fixed angular position to track their position but in a manner which allows slight axial or radial movement relative to the pipe.
U.S. Pat. No. 7,412,890 to Johnson (hereinafter the '890 patent) relates to a method and apparatus for detecting cracks in pipe welds comprising flooding a volume adjacent to the outer pipe surface with water, then using phased array ultrasound to scan the pipe surface. The apparatus has a rectangular cavity that has its open bottom surface pressed against the pipe surface and is flooded with water. The ultrasound array is positioned at the top of the cavity. Phased-array data collection methods are used.
U.S. Pat. No. 5,515,298 to Bicz (hereinafter the '298 patent) relates to an apparatus for performing ultrasound scanning of a fingerprint or other object placed on a concave surface. The apparatus projects ultrasound from an array of transducers through an array of pinholes (one per transducer) and against the concave interior of the surface on which the fingerprint rests. The transducers then derive characteristics of the fingerprint from the reflection and scattering of the spherical waveform produced by the pinhole. The apparatus appears to depend on the known structure of the convexo-concave lens structure of the support on which the fingerprint rests.
U.S. Pat. No. 6,896,171 to Den Boer et al (hereinafter the '171 patent) relates to an apparatus for performing EMAT (electromagnetic acoustic transducer) scanning of a freshly-made pipe weld while still hot. The apparatus may include an array of EMAT transmitter and receiver coils positioned on a ring structure around the outer surface of the pipe. No post-processing algorithm details are disclosed. The apparatus is described as being able to detect the presence of weld defects, and gives some information as to their size, but neither images, precise locations, nor are any further details of defects discussed in the description.
US App. Pub. No. 2009/0158850 to Alleyne et al (hereinafter the '850 publication) relates to a method and apparatus for inspecting pipes wherein the pig apparatus is inserted into the bore of the pipe. Ultrasound transducers are pressed against the inner walls of the pipe and use guided waves (e.g. Lamb waves) of ultrasound within the material of the pipe wall itself to detect defects. Data collection and processing appears to be based on a full matrix capture technique from which different wave modes may be extracted, although a phased-array data collection technique may also be used.
US App. Pub. No. 2009/0078742 to Pasquali et al. (hereinafter the '742 publication) relates to a method and apparatus for inspecting multi-walled pipes, such as those used for undersea transport of hot or cold fluids. The method involves placing an ultrasound probe against the inner pipe surface and scanning at various intervals as the probe rotates around the inner circumference of the pipe wall. The apparatus is a probe positioned at the end of a rotatable arm, which positions the probe within the pipe and then rotates it about the circumference of the inner wall. The '742 publication also discloses methods of positioning the probe at various angles relative to the pipe surface. However, it appears to only teach the use of probes that are displaced from the weld in the pipe's axial direction, and are angled forward or backward toward the location of the pipe weld.
Additional prior art references include U.S. Pat. No. 7,762,136 to Ume, Ifeanyi C. et al., which teaches ultrasound systems and methods for measuring weld penetration depth in real time and off line, U.S. Pat. No. 7,694,569 to McGrath, Matthew et al. which teaches a phased array ultrasonic water wedge apparatus, U.S. Pat. No. 7,694,564 to Brignac, Jacques L. et al. which teaches a boiler tube inspection probe with centering mechanism and method of operating the same, U.S. Pat. No. 6,935,178 to Prause, Reinhard which teaches a device for inspecting pipes using ultrasound, U.S. Pat. No. 6,734,604 to Butler, John V. et al. which teaches a multimode synthesized beam transduction apparatus, U.S. Pat. No. 4,872,130 to Pagano, Dominick A., which teaches an automated in-line pipe inspection system JP 2004028937 to Furukawa, T. et al., which teaches a method for measuring the shape of a welded pipe.